The present invention relates to an apparatus for testing a digital satellite communication system in which digital satellite communication units or terminals are interconnected by multiple channels and, more particularly, to a system testing apparatus which, by using a single satellite delay simulator, applies a delay to all of the communication terminals that are operated on independent clocks. Further, the present invention is concerned with an improved satellite delay simulator.
Two different approaches are available for testing a digital satellite communication system having a plurality of digital satellite communication terminals which are interconnected by multiple channels. One of them is to allocate a single satellite delay simulator to each of the channels of the communication system. Although this kind of scheme is successful in testing the system without effecting the independence of the individual clocks on which the communication units are operated, the number of delay simulators has to be increased with the number of channels resulting in the overall size and cost of the testing equipment being increased. The other approach known in the art is such that all the channels share a single satellite delay simulator. This is advantageous over the one-to-one allocation scheme in that it cuts down the cost and size of the testing equipment. However, the single delay simulator scheme has a drawback that the clocks each being assigned to a particular communication terminal have to be synchronized to the clock of the single delay simulator without exception and, hence, the testing conditions are different from the actual conditions in which the system is operated.